1. Field of the Invention
The present invention relates to a magnetic recording medium in which a recording layer is formed in a predetermined concavo-convex pattern to form recording elements as a convex portion of the concavo-convex pattern, and to a magnetic recording and reproducing apparatus comprising the magnetic recording medium.
2. Description of the Related Art
Conventionally, in a magnetic recording medium such as a hard disk, the areal density has been significantly increasing through employing finer magnetic particles composing a recording layer, changing materials, and improving microprocessing of a head, and a further improvement of the areal density is expected from this time forward. However, problems such as limitations on head processing, erroneous recording to a track adjacent to a target track caused by a spread recording magnetic field of a magnetic head, and crosstalk upon reproducing have become apparent, and an improvement of the areal density is no longer possible by means of conventional techniques.
Therefore, as a candidate for a magnetic recording medium which may provide a higher areal density, a discrete track medium and a patterned medium having a recording layer formed in a concavo-convex pattern to form recording elements as a convex portion of the concavo-convex pattern have been proposed (see, for example, Japanese Patent Laid-Open Publication No. Hei 9-97419). As the areal density increases, the magnetic gap between a magnetic head and a magnetic recording medium becomes smaller. For a magnetic recording medium such as a discrete track medium or a patterned medium, in which an areal density of 200 Gbpsi or more is estimated, a magnetic gap of 15 nm or less may be required.
In a magnetic recording medium such as a hard disk, surface flatness is an important factor to prevent a magnetic head crash. For a discrete track medium and a patterned medium having a high areal density and a small magnetic gap, surface flatness is particularly important. In this respect, preferably, the concave portion between recording elements is filled with a non-magnetic filler element and the top surface of the recording element and the filler element are flattened. Examples of the method for filling concave portions with a filler element include a deposition method such as a sputtering method, a CVD (Chemical Vapor Deposition) method, or an IBD (Ion Beam Deposition) method. Examples of the flattening method include a processing method such as a CMP (Chemical Mechanical Polishing) method or a dry etching method (see, for example, Japanese Patent Laid-Open Publication No. Hei 12-195042 and Japanese National Publication of PCT Application No. Hei 14-515647).
On the other hand, when the surface is excessively flat, stiction of a magnetic head to the surface of a magnetic recording medium tends to occur, causing an increase in the occurrence of a magnetic head crash. In this respect, a magnetic head crash caused by stiction has been conventionally prevented by applying texture processing to the surface of a substrate and depositing a recording layer and other layers one after another thereon to form a fine concavo-convex structure on the surface of a magnetic recording medium following the texture processing pattern on the substrate. For a discrete track medium and a patterned medium, a configuration having a step between the top surface of a recording element and the top surface of a filler element has been disclosed (see, for example, Japanese Patent Laid-Open Publication No. Hei 1-279421). In this case, a technique utilizing the step for imparting a texture effect may be conceivable.
However, if the concavo-convex structure is formed on the surface by means of a technique for applying the texture processing to a substrate, the surface may become a wavy distorted shape having a period of about 100 nm to 2 μm. It would be difficult for a magnetic head to fly along the wavy distortion having a period of about 100 nm to 2 μm. And the wavy distortion may directly cause the variation of a magnetic gap. In the generation in which a magnetic gap was 25 nm or more, such a variation of the magnetic gap did not cause practical problems. However, if the magnetic gap is reduced to 15 nm or less, the effects caused by the variation of the magnetic gap may become practically inadmissible.
Also, even when the texture processing is applied to the surface of a substrate, the fine concavo-convex structure following the texture processing pattern on the substrate may be removed if the space between the recording elements is filled with the filler element and the top surfaces of the recording element and the filler element are flattened. Therefore, the formation of the desired fine concavo-convex structure on the surface is difficult by means of this technique.
In the case where a technique for forming a step between the top surface of the recording element and the top surface of the filler element is employed, the air film stiffness between a magnetic head and the surface of a magnetic recording medium becomes excessively small, causing the flying state of the magnetic head unstable. Therefore, the flying height of the magnetic head tends to be largely changed by disturbance, and sufficient reliability may not be obtained.